world trade center timeline : 09/11/2001

9.50am

The south tower of the World Trade Center collapses, plummeting into the streets below. A massive cloud of dust and debris forms and slowly drifts away from the building.

There are rumours of both a third plane and a bomb. These are untrue.

Slate:

"When a fire ignites in a large building, its steel core does not melt, but over time it weakens. As the steel supporting the floors collapses, a "pancaking" effect will result, with each of the upper floors collapsing onto the floor below. This is why the disintegration of the towers was not limited to the top floors. With the accumulated weight of each collapsed floor, the stacked floors continued to fall. This explains why the building collapsed vertically, rather than tipping over"

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